gdb/fork-child.c

   1 /* Fork a Unix child process, and set up to debug it, for GDB.
   2    Copyright 1990, 1991, 1992 Free Software Foundation, Inc.
   3    Contributed by Cygnus Support.
   4
   5 This file is part of GDB.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 #include "defs.h"
  22 #include "frame.h"  /* required by inferior.h */
  23 #include "inferior.h"
  24 #include "target.h"
  25 #include "wait.h"
  26 #include "gdbcore.h"
  27 #include "serial.h" /* For job_control.  */
  28 #include "terminal.h"           /* For new_tty */
  29
  30 #include <signal.h>
  31
  32 #ifdef SET_STACK_LIMIT_HUGE
  33 #include <sys/time.h>
  34 #include <sys/resource.h>
  35
  36 extern int original_stack_limit;
  37 #endif /* SET_STACK_LIMIT_HUGE */
  38
  39 extern char **environ;
  40
  41 /* Start an inferior Unix child process and sets inferior_pid to its pid.
  42    EXEC_FILE is the file to run.
  43    ALLARGS is a string containing the arguments to the program.
  44    ENV is the environment vector to pass.  Errors reported with error().  */
  45
  46 #ifndef SHELL_FILE
  47 #define SHELL_FILE "/bin/sh"
  48 #endif
  49
  50 void
  51 fork_inferior (exec_file, allargs, env, traceme_fun, init_trace_fun)
  52      char *exec_file;
  53      char *allargs;
  54      char **env;
  55      void (*traceme_fun) PARAMS ((void));
  56      void (*init_trace_fun) PARAMS ((int));
  57 {
  58   int pid;
  59   char *shell_command;
  60   char *shell_file;
  61   static char default_shell_file[] = SHELL_FILE;
  62   int len;
  63   int pending_execs;
  64   int terminal_initted;
  65   /* Set debug_fork then attach to the child while it sleeps, to debug. */
  66   static int debug_fork = 0;
  67   /* This is set to the result of setpgrp, which if vforked, will be visible
  68      to you in the parent process.  It's only used by humans for debugging.  */
  69   static int debug_setpgrp = 657473;
  70   char **save_our_env;
  71
  72   /* If no exec file handed to us, get it from the exec-file command -- with
  73      a good, common error message if none is specified.  */
  74   if (exec_file == 0)
  75     exec_file = get_exec_file(1);
  76
  77   /* The user might want tilde-expansion, and in general probably wants
  78      the program to behave the same way as if run from
  79      his/her favorite shell.  So we let the shell run it for us.
  80      FIXME, this should probably search the local environment (as
  81      modified by the setenv command), not the env gdb inherited.  */
  82   shell_file = getenv ("SHELL");
  83   if (shell_file == NULL)
  84     shell_file = default_shell_file;
  85
  86   /* Multiplying the length of exec_file by 4 is to account for the fact
  87      that it may expand when quoted; it is a worst-case number based on
  88      every character being '.  */
  89   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop*/ 12;
  90   /* If desired, concat something onto the front of ALLARGS.
  91      SHELL_COMMAND is the result.  */
  92 #ifdef SHELL_COMMAND_CONCAT
  93   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
  94   strcpy (shell_command, SHELL_COMMAND_CONCAT);
  95 #else
  96   shell_command = (char *) alloca (len);
  97   shell_command[0] = '\0';
  98 #endif
  99   strcat (shell_command, "exec ");
 100
 101   /* Now add exec_file, quoting as necessary.  */
 102   {
 103     char *p;
 104     int need_to_quote;
 105
 106     /* Quoting in this style is said to work with all shells.  But csh
 107        on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
 108        to.  */
 109     p = exec_file;
 110     while (1)
 111       {
 112         switch (*p)
 113           {
 114           case '\'':
 115           case '"':
 116           case '(':
 117           case ')':
 118           case '$':
 119           case '&':
 120           case ';':
 121           case '<':
 122           case '>':
 123           case ' ':
 124           case '\n':
 125           case '\t':
 126             need_to_quote = 1;
 127             goto end_scan;
 128
 129           case '\0':
 130             need_to_quote = 0;
 131             goto end_scan;
 132
 133           default:
 134             break;
 135           }
 136         ++p;
 137       }
 138   end_scan:
 139     if (need_to_quote)
 140       {
 141         strcat (shell_command, "'");
 142         for (p = exec_file; *p != '\0'; ++p)
 143           {
 144             if (*p == '\'')
 145               strcat (shell_command, "'\\''");
 146             else
 147               strncat (shell_command, p, 1);
 148           }
 149         strcat (shell_command, "'");
 150       }
 151     else
 152       strcat (shell_command, exec_file);
 153   }
 154
 155   strcat (shell_command, " ");
 156   strcat (shell_command, allargs);
 157
 158   /* exec is said to fail if the executable is open.  */
 159   close_exec_file ();
 160
 161   /* Retain a copy of our environment variables, since the child will
 162      replace the value of  environ  and if we're vforked, we have to
 163      restore it.  */
 164   save_our_env = environ;
 165
 166   /* Tell the terminal handling subsystem what tty we plan to run on;
 167      it will just record the information for later.  */
 168
 169   new_tty_prefork (inferior_io_terminal);
 170
 171   /* It is generally good practice to flush any possible pending stdio
 172      output prior to doing a fork, to avoid the possibility of both the
 173      parent and child flushing the same data after the fork. */
 174
 175   fflush (stdout);
 176   fflush (stderr);
 177
 178 #if defined(USG) && !defined(HAVE_VFORK)
 179   pid = fork ();
 180 #else
 181   if (debug_fork)
 182     pid = fork ();
 183   else
 184     pid = vfork ();
 185 #endif
 186
 187   if (pid < 0)
 188     perror_with_name ("vfork");
 189
 190   if (pid == 0)
 191     {
 192       if (debug_fork)
 193         sleep (debug_fork);
 194
 195       /* Run inferior in a separate process group.  */
 196       debug_setpgrp = gdb_setpgid ();
 197       if (debug_setpgrp == -1)
 198          perror("setpgrp failed in child");
 199
 200 #ifdef SET_STACK_LIMIT_HUGE
 201       /* Reset the stack limit back to what it was.  */
 202       {
 203         struct rlimit rlim;
 204
 205         getrlimit (RLIMIT_STACK, &rlim);
 206         rlim.rlim_cur = original_stack_limit;
 207         setrlimit (RLIMIT_STACK, &rlim);
 208       }
 209 #endif /* SET_STACK_LIMIT_HUGE */
 210
 211       /* Ask the tty subsystem to switch to the one we specified earlier
 212          (or to share the current terminal, if none was specified).  */
 213
 214       new_tty ();
 215
 216       /* Changing the signal handlers for the inferior after
 217          a vfork can also change them for the superior, so we don't mess
 218          with signals here.  See comments in
 219          initialize_signals for how we get the right signal handlers
 220          for the inferior.  */
 221
 222       /* "Trace me, Dr. Memory!" */
 223       (*traceme_fun) ();
 224
 225       /* There is no execlpe call, so we have to set the environment
 226          for our child in the global variable.  If we've vforked, this
 227          clobbers the parent, but environ is restored a few lines down
 228          in the parent.  By the way, yes we do need to look down the
 229          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 230       environ = env;
 231       execlp (shell_file, shell_file, "-c", shell_command, (char *)0);
 232
 233       fprintf (stderr, "Cannot exec %s: %s.\n", shell_file,
 234                safe_strerror (errno));
 235       fflush (stderr);
 236       _exit (0177);
 237     }
 238
 239   /* Restore our environment in case a vforked child clob'd it.  */
 240   environ = save_our_env;
 241
 242   /* Now that we have a child process, make it our target, and
 243      initialize anything target-vector-specific that needs initializing.  */
 244   (*init_trace_fun)(pid);
 245
 246   init_thread_list();
 247
 248 #ifdef CREATE_INFERIOR_HOOK
 249   CREATE_INFERIOR_HOOK (pid);
 250 #endif
 251
 252 /* The process was started by the fork that created it,
 253    but it will have stopped one instruction after execing the shell.
 254    Here we must get it up to actual execution of the real program.  */
 255
 256   inferior_pid = pid;           /* Needed for wait_for_inferior stuff below */
 257
 258   clear_proceed_status ();
 259
 260   /* We will get a trace trap after one instruction.
 261      Continue it automatically.  Eventually (after shell does an exec)
 262      it will get another trace trap.  Then insert breakpoints and continue.  */
 263
 264 #ifdef START_INFERIOR_TRAPS_EXPECTED
 265   pending_execs = START_INFERIOR_TRAPS_EXPECTED;
 266 #else
 267   pending_execs = 2;
 268 #endif
 269
 270   init_wait_for_inferior ();
 271
 272   terminal_initted = 0;
 273
 274   while (1)
 275     {
 276       stop_soon_quietly = 1;    /* Make wait_for_inferior be quiet */
 277       wait_for_inferior ();
 278       if (stop_signal != SIGTRAP)
 279         {
 280           /* Let shell child handle its own signals in its own way */
 281           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 282           resume (0, stop_signal);
 283         }
 284       else
 285         {
 286           /* We handle SIGTRAP, however; it means child did an exec.  */
 287           if (!terminal_initted)
 288             {
 289               /* Now that the child has exec'd we know it has already set its
 290                  process group.  On POSIX systems, tcsetpgrp will fail with
 291                  EPERM if we try it before the child's setpgid.  */
 292
 293               /* Set up the "saved terminal modes" of the inferior
 294                  based on what modes we are starting it with.  */
 295               target_terminal_init ();
 296
 297               /* Install inferior's terminal modes.  */
 298               target_terminal_inferior ();
 299
 300               terminal_initted = 1;
 301             }
 302           if (0 == --pending_execs)
 303             break;
 304           resume (0, 0);                /* Just make it go on */
 305         }
 306     }
 307   stop_soon_quietly = 0;
 308
 309   /* We are now in the child process of interest, having exec'd the
 310      correct program, and are poised at the first instruction of the
 311      new program.  */
 312 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 313   SOLIB_CREATE_INFERIOR_HOOK (pid);
 314 #endif
 315 }